1. Field of the Invention
This invention relates to and has among its objects the provision of novel methods and apparatus for melting icebergs. It is a particular object of the invention to provide both fresh water and mechanical energy from the melting of icebergs. Further objects of the invention will be evident from the following description wherein parts and percentages are by weight unless otherwise specified.
2. Description of the Prior Art
The most productive agricultural regions are arid regions because they are rich in solar energy and their soils are high in nutrients. However, these agriculturally productive arid regions must obtain irrigation water from humid areas. To significantly extend crop acreage, therefore, it is necessary to expand irrigation.
One solution proposed for providing an inexpensive source of irrigation water for arid regions is the use of melt water from icebergs. The annual yield of fresh water from icebergs is estimated at 12,000 cubic kilometers, the total world iceberg accumulation being six times this amount. Annual yield of fresh water from Antartic icebergs alone would provide sufficient water to irrigate about 90 million hectares or 40% of currently irrigated land.
A number of modes of iceberg transport have been disclosed: Science Digest, Vol. 39, page 1 (1956); Water Resources Journal, Vol. 100, page 1 (1974); Bull. Atom. Scient., Vol. 29, page 35 (1973); Journal of Glaciology, Vol. 12, page 207 (1973); Ocean Industry, Vol. 8, page 28 (1973); and New Scientist, Vol. 75, page 11 (1977). It has been calculated that icebergs could be delivered to the United States at a cost that would make them highly attractive as a source of both irrigation and drinking water.
The major problem in obtaining water from icebergs in the large expenditure of energy required to melt an iceberg. Indeed, the energy necessary to melt an iceberg is about 2,000 times greater than the energy needed to transport it. Solar energy has been considered, but it is postulated that direct contact of the desert sun of Saudi Arabia on an iceberg would melt only approximately 10 vertical meters of iceberg per year. Another suggestion as an energy source is waste heat from coastal electric power plants. However, this would require bringing an iceberg close to coastal boundaries, which presents some difficulty because of the depth of an iceberg and the necessity for running pipe lines to convey the source of waste heat to the iceberg and the fresh water from the iceberg to the coast.
The oceans of the world represent a vast source of solar energy and the idea of recovering this energy is old in the art, being first proposed in 1881. Ocean Thermal Energy Conversion (hereinafter referred to as OTEC) has been described recently. Basically, OTEC involves converting the difference in temperatures of warmer surface sea water and cooler deep sea water into mechanical energy (Solar Energy, Vol. 18, pages 81-92 (1976)). In closed cycle OTEC a fluid, such as ammonia or a halogenated hydrocarbon, is heated with warm seawater through a heat exchanging boundary to vaporize it. After expansion through a turbine, the vapor is condensed on a heat exchanging surface with cold seawater (Mechanical Engineering, Vol. 88, page 41, (1966); Chem. Eng. News, Vol. 54, page 19 (1976); and Solar Energy, Vol. 20, page 259 (1978)). Open cycle OTEC (U.S. Pat. No. 3,967,449) is a simpler concept than closed cycle OTEC since cool seawater is employed directly to condense vaporized warm seawater. However, even open cycle OTEC has the disadvantage that heat exchangers are required in order to produce fresh water from seawater.